Airport run-off feeding bacteria for WWT

ITT Flygt has supplied a range of pumps for an innovative wastewater treatment plant on the outskirts of Oslo

De-icing glycol from airports is usually considered to be an environmental
problem. However, now at one Norwegian airport, the used glycol is collected
for use as nutrient for bacteria that process wastewater in a nearby treatment
plant.

The Gardermoen plant treats wastewater from the airport, from local industry
and from the 20,000 or so people who live in the surrounding counties of Ullensaker
and Nannestad. The amount of wastewater produced by the airport and its restaurants
and toilets takes up about a third of the plant's capacity.

'The plant has worked well from the start and has managed to keep above the
high standards required,' said Willy Slora, technical manager.

'Norwegian authorities have placed rigid criteria on the efficiency of waste
treatment here, demanding 95% removal of phosphorus, 90% removal of organic
material and 70% removal of nitrogen. There are only four or five other plants
in Norway which remove nitrogen from wastewater,' he added.

Re-use of glycol
The plant receives about 5,000 metres³ of wastewater per day from the two
counties and the airport. It also receives glycol-containing wastewater from
the airport, which is the result of the de-icing of aircraft in winter months.

An important part of the denitrification process is the addition of the glycol
to the plant's bioculture reactors. The glycol is an important source of hydrocarbon
in the denitrification process and replaces the ethanol normally used. Apart
from being a sensible environmental solution, the re-use of glycol also saves
the plant considerable expense.

The plant was originally built to deal with the glycol-containing water as
an adjunct to wastewater treatment. No one expected that the glycol waste would
be sufficient for the plant's denitrification needs, so a container for storing
ethanol was installed. However, so far the container has not been used. There
has been more than enough glycol waste to feed the bioculture reactors.

The first phase in the treatment of wastewater removes the largest particles,
such as napkins, cotton wool and sanitary articles. These are pressed out mechanically
and sent to containers for storage and disposal at the local landfill. About
15 metres³ of this waste are dumped every fortnight. This is not a satisfactory
solution, Slora says. Future plans for the plant include building an incinerator
for burning the waste.

The remaining wastewater is sent through a grit-and-grease trap to remove sand
and fat, coffee grounds and smaller particles, and then on to two primary clarifier
basins.

A Flygt DS 3057, 2.2 kW submersible pump is installed in the primary clarifier
basin to pump floating sludge. From here the wastewater goes to the biological
part of the process, where it is pumped into two parallel lines, with seven
serially connected reactors or cells. These cells, which are seven metres deep,
are filled to 60% capacity with 'Kaldnes elements' - small, hollow plastic wheels,
10 millimetres in diameter, with a convoluted inner and outer surface, which
are kept in constant motion.

The bacterial cultures responsible for the biological degrading of the wastewater
are attached to the surface area of the Kaldnes elements. The addition of these
plastic elements greatly increases the concentration of bacteria in comparison
to a normal activated sludge process.

In the first reactors, the bioculture is aerated to remove organic material.
The aeration system is a coarse bubble system in stainless steel. In final reactors
in the series, nitrogen-containing compounds are converted to nitrogen gas,
which is released into the atmosphere.

The wastewater is treated chemically using aluminium in solution so that phosphates
are bound as particles. Small bubbles in the floatation basins make the particles
float to the surface so that they can be scraped off and sent to the sludge
treatment plant. The water is finally exposed to UV light to remove bacteria,
making it of acceptable quality to be used as drinking water for farm animals.

The sludge from the clarifier basin and flotation is mixed in a tank and carried
to a digester tank, and methane gas is collected from the process. This methane
is used as an energy source for drying the sludge and for heating the plant.
The sludge is finally air-dried in large drums at 600°C, producing granules
that can be used as a soil supplement on farms, in parks and garden areas.

Project details
The Gardermoen wastewater and water treatment plant uses ITT Flygt pumps and
mixers supplied by Purac, a Swedish company. The pumps and mixers have varying
capacities, depending on where in the system they are placed and the medium
in which they work.

At the intake, there are three Flygt CP 3201 pumps of 22kW, each with a capacity
of 10.8 metres³/min, and eight mixers. One of the pumps is run by a frequency
converter. In the grit-and-grease removal basin, there are two Flygt DP 3080
pumps, each with a power of 4 kW.

The water within each anoxic bioculture reactor is agitated by one Flygt SR
4430 mixer with a power of 4 kW, (14 mixers in total). These mixers keep the
culture and the Kaldnes elements in it moving constantly to ensure effective
biological degrading of the wastewater. A Flygt CP 3152 pump of 10.5 kW has
been installed to circulate the wastewater.

The sludge is mixed by one Flygt SR 4640, 3 kW and one SR 4630, 2 kW. Three
Flygt Ready pumps are used for taking samples of wastewater at different stages.